Chemistry Reference
In-Depth Information
high
P
H
2
O
P
H
2
O
low
T
T
CaAI
2
Si
2
O
8
CaAI
2
Si
2
O
8
NaAISi
3
O
8
NaAISi
3
O
8
KAISi
3
O
8
KAISi
3
O
8
Figure 3.7
Solidus and solvus of the feldspars.
Left, diagram under a high water pressure: solvus and solidus intersect so that the stability field of
feldspars forms two disjoint volumes (materialized by the isotherms).They are limited by the solvus
and toward high temperatures, by the solidus (tight hatch).
Right, diagram under low water pressure: the boundaries of the solidus are represented by a bold line.
The dome materialized by isotherms represents the two-feldspar field. The volume between the two
surfaces is the domain of mixed feldspar.
plagioclase
+ melt
T
T
alkali
feldspar
+ melt
L0
E
L1
L2
E
F
CaAl
2
Si
2
O
8
CaAl
2
Si
2
O
8
F
KAISi
3
O
8
NaAISi
3
O
8
NaAISi
3
O
8
KAISi
3
O
8
Figure 3.8
Liquidus of the feldspars (after Best 1982, modified) It is difficult to read this
diagram if it is oriented in the same way as the previous diagrams (left figure),
so it has been differently reoriented on the right figure.
